Maleic anhydride grafted EP(D)M's have not been used much for impact modification of polyesters because the transesterification reaction between polyesters and the maleic anhydride group of the MA-grafted-EP is a slow reaction and because EP based modifiers having a high level of maleic anhydride and a low viscosity have not been available. Recently, Dow Chemical Company has described both in U.S. Pat. No. 5,346,963 and PCT WO 94/25526 that substantially linear ethylene polymers produced by Dow "constrained geometry" catalysts and grafted with an unsaturated organic compound exhibit adhesive properties as well as impart desirable impact properties to various thermoplastic polymers blends such as polyamide or polyesters. Likewise in U.S. Pat. No. 5,705,565 Dow Chemical Company discloses blends of their maleated ethylene-octene copolymers with polyamide. In polybutylene terephthalate, these modifiers are however only effective as impact modifiers at treat levels around 20%. In order to be competitive with other modifiers such as core shell polybutadiene polymethacrylate polymers or MBS (methacrylate, butadiene stryrene copolymers), impact modification at lower treat levels is required. Surprisingly, we have observed that, the combination of a functionalized ethylene alpha-olefin copolymer and an ethylene alpha-olefin copolymer gives improved impact performances at lower treat levels versus a straight functionalized ethylene alpha-olefin copolymer having the same functionality level and same viscosity.
Art disclosed for US purposes includes WO 97/27259.